<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //声明变量
        let a;
        let b, c, d;
        let e = 100;
        let f = 521, g = 'iloveyou', h = [];

        //1.变量不能重复声明
        // let star = '张三';
        // let star = '小三';

        //2.块级作用域  全局，函数， eval
        //if else while for 后面的{}都是块级
        // {
        //     let girl = '小红';
        // }
        // console.log(girl);

        //3.不存在变量提升
        console.log(song);
        let song = '恋爱达人'

        //4.不影响作用域链
        {
            let school = '西安文理';
            function fn(){
                console.log(school);
            }
            fn()
        }
    </script>
</body>
</html>